1. Field of the Invention
This invention relates in general to offshore drilling, and in particular to equipment and methods for running conduit with an offshore rig.
2. Background of the Invention
When drilling subsea wells, a low pressure wellhead housing is installed with a string of conductor casing or pipe extending therefrom into the sea floor. A high pressure wellhead housing is then landed in the bore of the low pressure wellhead housing with another string casing extending therefrom to a deeper depth. Additional strings of casing that extend deeper into the subsea well, until at least one string reaches a production depth, are suspended from casing hangers landed within the bore of the high pressure housing. A tubing hanger is then landed for supporting a string of production tubing that receives the hydrocarbons from the subsea well after the deepest string of casing is perforated.
Typically, the tubing hanger is lowered into the subsea wellhead assembly through a riser extending from a vessel at the surface. In previous systems, the tubing hanger had downward facing shoulders that would land on an upward facing support within the subsea housing. The downward facing shoulders typically increased the outer diameter of the tubing hanger, and thus also increased the minimum allowable diameter of the riser through which the tubing hanger was lowered. In other previous systems, the retractable locking assemblies were located on the outer periphery of the tubing hanger so that the outer diameter of the tubing hanger was smaller than previous tubing hangers. These locking assemblies were typically actuated mechanically when landing within the subsea wellhead housing by profiles formed in the subsea wellhead assembly that would engage and actuate the locking assembly radially outward to land upon the support surfaces in the subsea wellhead assembly. However, these assemblies required the tubing hanger to be oriented properly for such actuation to occur.